Such apparatuses are generally known for traditional parts from the state of the art. Typically, such apparatuses are used to expand primarily metal tubular workpieces by internal fluid pressurization, frequently a liquid. Due to the confinement in a die, the expansion expands the wall of the workpiece until it rests against a contoured inside wall of a die. The contoured inside wall, which is also referred to as the die engraving, thus defines the eventual outer shape of a workpiece to be hydroformed.
A known apparatus for carrying out such a hydroforming processes typically comprises an at least two-part die that can be opened in order to load a tubular workpiece for the forming process. After closing the die, particularly by pressing an upper die part onto a lower die part, the means for sealing and filling/pressurizing are pressed against the open workpiece ends and the workpiece is deformed by the internal pressure that is thus produced. After such a forming step, and particularly the removal of the means mentioned above, the die can be opened and the formed workpiece can be removed.
Such hydroforming processes subject parts of the apparatus and tool to elastic deformation during the hydroforming process as a result of the comparatively high loads and pressures used for hydroforming. Such deformations can have an impact both on the dies and on the workpieces and adjoining parts of the apparatus.
Such deformations in particular can result in elastic compression of the dies, since an upper die part must be pressed against the lower die part with a die-closing force that is proportional to the internal pressure. As a result, a displacement, particularly a parallel displacement of the die and the workpiece inserted therein relative to other external parts of the apparatus may occur, for example by the means for sealing, such as plugs, or the means for filling and pressurizing that are pressed from the outside against the die or the tool ends during the forming operation.
In this way, process reliability may be reduced, for example due to reduced sealing properties of the means for sealing or filling/pressurizing. Likewise, wear may also be increased or dies may break.
In order to counteract this, it is already known to directly attach actuators for moving the means for sealing or filling and pressurizing the die. However, since the actuators therefore are directly supported on the die, the introduction of the stresses occurring during forming directly into the die causes tension and deformations, which likewise impair process reliability. For example, the weight of the actuators carried by the die can skew the means for sealing and/or filling/pressurizing. In addition, with such a solution the actuators are very complex to disassemble or reassemble when replacing the dies.
These problems mentioned above result in the fact that known apparatuses of the type described cannot be used for hydroforming microparts, such as tubular workpieces with dimensions, for example, of less than 3 mm in diameter, preferably less than 1 mm in diameter, because on such small workpieces the deformations have a stronger effect relative to the workpiece size than in conventional workpiece sizes. To this end, ratios of the wall thickness to the diameter of 0.02 to 0.2 can be used for microparts.